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I've tried doing some research on my own, but I'm coming up short. I'm looking at getting a Tesla wall charger installed in my home. Tesla recommends a 60A breaker so that the charger can run at 48A, although it can be adjusted to run on smaller circuits, all the way down to 15A.

My home has a main panel on one side of the house:

main panel image

I assume the breaker labeled 'House Panel' (90A) feeds the panel in the garage:

garage subpanel

If the garage panel can only support 90A, is there even really enough capacity to support a wall charger feeding off it? If the range takes ~30A and the dryer takes ~25A, we're at 90A-(30A+25A)=35A left over without running any lights, the fridge, TV, computer, etc.

Am I mistaken in thinking that, with the current configuration, if I wanted to power the wall charger off the garage panel, it would be inadvisable to go higher than, say, 20A, leaving 15A for the rest of the house? It's not impossible that all three big-current-draw items (dryer, range, charger) could be running simultaneously in normal use.

Supposing I wanted to run the charger at 40A, would I need to get the service back to the garage panel upgraded from 90A to 110A?

I'm out of my depth here and trying to make sense of these breaker ratings. Please, let me know if I have some fatal misconceptions. :-)

  • Keep in mind that just because an X Amp breaker is installed in the panel, X Amps are not necessarily being used on that circuit. In your case as long as the limit of the service (200 Amp it appears) is not being exceeded at any given point in time, you will not have issues. – jwh20 Jan 10 at 23:50
  • How far is the main panel from the garage? – JACK Jan 11 at 0:16
  • It really depends on the size of wire coming from the main 200 amp panel going to the garage from the 90 amp breaker. Finding the wire size here will give is a better idea what can be done. – Ed Beal Jan 11 at 0:17
  • @JACK Sadly, on the other side of the house. It's maybe 15 to 20 feet as the crow flies (the garage panel is on the interior garage wall closest to the main panel, but there's half a house in-between). – Reid Jan 11 at 0:25
  • Sadly I'm not sure what the wire size is, and it's now dark and raining outside. If the wire size was such that 110A was supported per code, that seems like it'd be the best case to me - just switch the breaker at the main panel to a higher-rated one, right? Otherwise getting more power to the garage could be ... difficult. – Reid Jan 11 at 0:27
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Go 60A on the Tesla charger.

You'll thank me later.

Your main panel has the capacity for it, so let's just bite the bullet and do it.

You can serve it out of the main panel without any trouble. 6/2 cable and you're done.

If you want, instead, you could replace that 90A cable with a 150A cable. At that point you can put the 60A charger in the big subpanel. I presume your awesome 40 space sub has 200A busing. However I think that will net out to a lot more money.

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